The present invention generally relates to the field of digital radios, and more particularly a sigma-delta-sigma modulator for analog-to-digital and digital-to-analog conversion in digital radios.
Current analog-to-digital and digital-to-analog conversion technology has spurious free dynamic ranges equivalent to 4 to 8 bits in the HF/VHF/UHF band. Required are 14 to 18 bits of performance to make digital signal processing directly at RF a reality. Additionally, there are numerous applications for ultra wide bandwidth, high resolution converters other than digital radios. There lies a need for high performance analog-to-digital (A/D) and digital-to-analog (D/A) converters for utilization in direct sampling digital receivers and direct digital transmitters.
As military budgets decline, there is an urgent need for communications equipment with greater flexibility that will support multiple modes of operation, signal bandwidths and waveforms while maintaining low cost, small size and high reliability. Additionally it is desirable to provide the capability to upgrade existing equipment for new requirements as they arise. The use of digital signal processing (DSP) techniques running under software control are therefore highly desirable, if not mandatory, to replace the analog circuits in communications equipment. Maximum use of DSP will support the inclusion of additional capabilities, provide greater flexibility, facilitate use of common modules, and provide more effective built-in-test (BIT). Digital techniques are also compatible with large scale integration (LSI) and very large scale integration (VLSI) technology, ensuring that continued improvements will result in size, cost and reliability.